1. Field of the Invention
The invention relates to a method of making a phosphorus acid copper salt. In particular, it relates to the copper salt of a phosphorodithioic acid.
2. Discussion of the Prior Art
Copper salts of phosphorodithioic acids are known compounds suitable for adding to lubricants, e.g., mineral lubricating oils, to impart oxidation resistant properties. For instance, see U.S. Pat. No. 2,552,570, which is incorporated herein by reference.
That same patent discloses that compounds of the type EQU (RO).sub.2 P(S)SCu
where R may be alkyl such as 2-ethylhexyl, and the like can be made by reacting, for example, a dialkyl phosphorodithioic acid with Cu.sub.2 O: EQU 2(RO).sub.2 P(S)SH+Cu.sub.2 O.fwdarw.(RO).sub.2 P(S)SCu+H.sub.2 O.
However, the salts made by this process are darkly colored products, indicative of contamination by divalent copper salts.
S. L. Lawton et al., Inorganic Chemistry, Vol. 11, No. 3, pages 612-618, 1972, teach a method of making copper (1) diisopropyl phosphorodithioate which comprises reacting an aqueous solution of cuprous chloride, containing sufficient ammonia to promote dissolution of the solid, with an aqueous solution of ammonium diisopropyl phosphorodithioate.
U.S. Pat. No. 2,552,570, incorporated herein by reference partly to establish utility of the compounds made by the improved method, describes the compositions used and the tests employed to establish utility.